Power substations typically include a plurality of buses each having a plurality of feeders coupled thereto. The feeders are coupled to and supply power typically to industrial and residential customers. Each feeder typically has at least one circuit breaker and a relay associated with that circuit breaker. The relay detects a predetermined condition, such as a fault, and sends a signal to open or "trip" the circuit breaker associated with that relay so that the feeder can no longer deliver power to the load coupled to it.
As a safety precaution, backup protection must be provided for relay and circuit breaker failure or malfunction. Conventionally, backup protection used in power substations required dedicated backup devices and dedicated wiring which increased the cost of providing backup protection and increased the amount of space required to implement such backup protection. In addition, conventional backup protection systems indiscriminately rendered more of the substation inoperable than was necessary. For example, conventional backup protection for the failure of the relays in the feeders included at least one additional relay located upstream of the feeder relays. If a fault occurred on a particular feeder and the relay associated with that feeder malfunctioned or failed to detect the fault, the upstream relay would eventually detect the fault and trip all of the circuit breakers downstream of it. Thus, all of the feeders would be disabled, not just the feeder in which the relay failed.
Conventional backup protection for circuit breakers in a power substation typically provided backup protection for the transformer's circuit breakers and not the individual circuit breakers located in the feeders. Backup systems required one device, such as a breaker failure relay per circuit breaker to detect the malfunction or failure of the circuit breaker associated with the device. The device would monitor the status of a circuit breaker associated with the device and start a timer. If the circuit breaker was not open when the timer expired, the device, which was typically externally wired to additional devices that would be wired to trip additional circuit breakers, would generate an output signal to the other devices to trip the additional circuit breakers. Alternatively, some devices monitored the current flowing through the circuit breaker associated with the device to determine if the circuit breaker failed to open. Because of the need for additional devices and wiring, the space required to implement such backup protection systems increased as well as the cost of implementing such systems.
In addition, to reclose circuit breakers once the predetermined condition had been cleared, conventional systems utilized a separate device such as a reclosing relay associated with each circuit breaker. The device would start a timing sequence any time the circuit breaker associated with it opened. When the timing sequence expired, and assuming other supervisory conditions were satisfied, the device would output a signal to close the circuit breaker associated with it. As already discussed with reference to the backup protection for circuit breaker failure, because one device was associated with each circuit breaker, the same disadvantages regarding space and cost exist.
It is thus desirable to provide a control system that detects the failure of a relay in a feeder and generates a backup command to trip only the circuit breaker associated with the failed relay thereby leaving the other feeders in which no failure or malfunction has been detected unaffected. It is also desirable to provide a control system that is integrated and provides one time reference to allow for a more uniform response. It is also desirable to provide a control system that allows for more accurate and uniform reclosing of circuit breakers after a fault has been cleared Finally, it is desirable to provide a control system that requires minimal space for its implementation, that is less expensive than conventional backup protection systems and can be easily reconfigured to changing requirements.